1. Field of the Invention
The present invention relates to a technique of correcting exposure unevenness caused by an external light change (generally referred to as a flicker) which occurs in shooting in an image capturing apparatus such as a digital camera.
2. Description of the Related Art
Recently, along with the improvement of sensitivity of the image sensor of a digital camera, it is possible to shoot with a high-speed shutter (in a short exposure time) even under an artificial light source indoors or the like. When shooting with the high-speed shutter under a flicker light source, however, an external light change due to the flicker light source causes the variation in brightness for each frame in continuous shooting. Furthermore, in shooting with a so-called rolling shutter which sequentially exposes image capturing regions for each predetermined region, the external light change due to the flicker light source causes exposure unevenness within a screen.
In Japanese Patent Laid-Open No. 2004-193922, a technique of performing exposure at a timing with the largest light amount in a light emission cycle of a light source is proposed for this problem. According to this technique, since each shooting is performed at the timing with the largest light amount in the light emission cycle of the light source also in continuous shooting, the variation in brightness for each frame does not occur. Moreover, since the change in the light amount is small near the timing with the largest light amount in the light emission cycle, exposure unevenness within the screen can also be reduced.
In the related art disclosed in Japanese Patent Laid-Open No. 2004-193922 described above, however, since shooting is not performed at a user intended timing but is performed in accordance with the timing with the largest light amount in the light emission cycle of the light source, a photo opportunity may be missed. In some cases, the user may not want to miss the photo opportunity in spite of the occurrence of certain exposure unevenness or the like due to a flicker. However, the user cannot determine easily whether control to suppress an influence of the flicker or control not to miss the photo opportunity should be performed because information for deciding it is not available.
There is also a technique of correcting an image to an image with suppressed influence of the flicker by image processing after shooting. However, the variation in noise becomes conspicuous even though the variation in brightness or exposure unevenness is suppressed by correction. Also, in this case, the user cannot determine easily whether the control to suppress the influence of the flicker or control to make the variation in noise less conspicuous should be performed.